GENETIC ENGINEERING Flashcards
Genetic engineering
Changing the genetic material of an organism by removing, changing or inserting individual genes
Biotechnology is the application of
biological organisms, systems or processes to manufacturing and service industries. Genetic engineering involves the transfer of genes from one organism to (usually) an unrelated species. Both processes often make use of bacteria because of their ability to make complex molecules (e.g. proteins) and their rapid reproduction rate.
Use of bacteria in biotechnology and genetic engineering
Bacteria are useful in biotechnology and genetic engineering because: • they can be grown and manipulated without raising ethical concerns; • they have a genetic code that is the same as all other organisms, so genes from other animals or plants can be successfully transferred into bacterial DNA.
Bacterial DNA is in the form of a circular
strand and also small circular pieces called plasmids. Scientists have developed techniques to cut open these plasmids and insert sections of DNA from other organisms into them. When the bacterium divides, the DNA in the modified plasmid is copied, including the ‘foreign’ DNA. This may contain a gene to make a particular protein.
Production of ethanol for biofuels
In Chapter 12, the anaerobic respiration of glucose to alcohol is described as a form of fermentation. Micro-organisms that bring about fermentation are using the chemical reaction to produce energy, which they need for their living processes. Yeast is encouraged to grow and multiply by providing nutrients such as sugar. Oxygen or air is excluded to maintain an anaerobic process. Ethanol is a waste product. An optimum pH and temperature are maintained for the yeast being cultured. Some countries produce ethanol in this way as a renewable source of energy (biofuel) for motor cars, replacing non-renewable petrol.
Bread-making
Yeast is used in bread-making and brewing because of the products produced when it respires. The yeast is mixed with water and sugar to activate it. The mixture is added to flour to make dough. This is left in a warm place to rise. The dough rises because the yeast is releasing carbon dioxide, which gets trapped in the dough. A warm temperature is important because respiration is controlled by enzymes (see Chapter 5). When the dough is cooked, the high temperature kills the yeast and any ethanol formed evaporates. Air spaces are left where the carbon dioxide was trapped. This gives the bread a light texture.
The use of lactase to produce lactose-free milk
Lactose is a type of sugar found in milk and dairy products. Some people suffer from lactose intolerance, a digestive problem in which the body does not produce enough of the enzyme lactase. As a result, the lactose remains in the gut, where it is fermented by bacteria, causing symptoms such as flatulence (wind), diarrhoea and stomach pains. Many foods contain dairy products, so people with lactose intolerance cannot eat them, or suffer the symptoms described above. However, lactose-free milk is now produced using the enzyme lactase.
The lactase can be produced on a large scale by fermenting yeasts or fungi. The fermentation process is
shown in Figure 20.1. A simple way to make lactose-free milk is to add lactase to milk. The enzyme breaks down lactose sugar into two monosaccharide sugars: glucose and galactose. Both can be absorbed by the intestine. An alternative, large-scale method is to immobilise lactase on the surface of beads. The milk is then passed over the beads and the lactose sugar is effectively removed. This method avoids having the enzyme molecules in the milk because they remain on the beads.
Penicillium
Penicillium and the production of the antibiotic penicillin Some micro-organisms, such as the fungus Penicillium, produce complex organic compounds called antibiotics. The fungus is grown on a large scale (see Figure 20.1), then put under stress by reducing the nutrient supply. This causes it to secrete penicillin, which can be filtered off.
How fermenters are used in the production of penicillin
The fermenter (Figure 20.1) is a large, sterile container with a stirrer, a pipe to add feedstock (molasses or corn-steep liquor) and air pipes to blow air into the mixture. The fungus Penicillium is added and the liquid is maintained at around 26 ° C and a pH of 5– 6. Sterile conditions are essential to prevent ‘foreign’ bacteria or fungi getting into the system, as they can completely disrupt the process. As the nutrient supply diminishes, the fungus begins to secrete antibiotics into the medium. The nutrient fluid containing the antibiotic is filtered off and the antibiotic is extracted by crystallisation or other methods.
Genetic engineering
The production of human insulin – the human insulin gene is inserted into bacteria. Human insulin does not trigger allergic reactions in the way that animal insulin can, and is acceptable to people with a range of religious beliefs.
- The insertion of genes into crop plants to give them resistance to herbicides (weedkillers) – this enables the farmer to spray the crop to kill weeds, without damaging the crop, and may reduce the use of herbicides. • The insertion of genes into crop plants to give them resistance to insect pests – the gene enables the plant to produce a poison that makes it resistant to attack by insect larvae.
- The insertion of genes into crop plants to provide additional vitamins – golden rice is a variety of rice that has had a gene for beta-carotene (a precursor of vitamin A) inserted. Golden rice is grown particularly in countries where vitamin A deficiency is a problem and where rice is a staple food. This deficiency often leads to blindness.
Using genetic engineering to put human insulin genes into bacteria
1 Human cells with genes for healthy insulin are selected.
2 A chromosome (which is a length of DNA) is removed from the cell.
3 The section of DNA representing the insulin gene is cut from the chromosome using restriction endonuclease enzyme. The DNA has sticky ends.
4 A suitable bacterial cell is selected. Some of its DNA is in the form of circular plasmids.
5 All the plasmids are removed from the bacterial cell.
6 The plasmids are cut open using the same restriction endonuclease enzyme.
7 The human insulin gene is inserted into the plasmids using ligase enzyme, forming recombinant plasmids.
8 The plasmids are returned to the bacterial cells (only one is shown in the diagram).
9 The bacterial cells are allowed to reproduce in a fermenter. All the cells produced contain plasmids with the human insulin gene. The bacteria can now produce human insulin on a commercial scale.
Disadvantages:
- The vectors for delivering recombinant DNA contain genes for antibiotic resistance. If these managed to get into potentially harmful bacteria, it might make them resistant to antibiotic drugs. • GM food could contain pesticide residues or substances that cause allergies.
- The precursor of vitamin A in golden rice could change into other, toxic chemicals once eaten.
- There is a risk of a reduction in biodiversity as a result of the introduction of GM species.
- Subsistence farmers could also be tied to large agricultural suppliers that may then manipulate seed prices.
Advantages of genetically modifying crops
- The aim of most genetic modification is to increase yields through the insertion of genes giving crops herbicide resistance and insect pest resistance. Genetically modified (GM) maize has resistance to pests and herbicides. GM soya has been modified to make it herbicide resistant.
- It is possible to improve the protein, mineral or vitamin content of food. Golden rice has a gene enabling it to produce a precursor of vitamin A. GM soya has an increased nutritional value.
- It is possible to improve the keeping qualities of some products, e.g. the storage properties of GM soya, through modification of its fat molecules using inserted genes. GM tomatoes have had a gene deleted that is responsible for fruit softening, extending their storage life.
